This disclosure relates to liquid fuel reformers and, more particularly, to such reformers that include a fuel vaporizer for vaporizing, or evaporating, a liquid fuel prior to its introduction into a gas phase reforming reaction zone.
A liquid fuel gas phase reformer is a chemical reactor in which a gaseous reformable reaction mixture containing a vaporized liquid fuel such as methanol, ethanol, distillate, naphtha, kerosene, gasoline, diesel, bio-diesel, etc., or combination thereof, and an oxygen-containing gas, typically air, and in the case of a steam reformer or autothermal reformer, water as steam, is converted in the gas phase into a hydrogen-rich reformate, commonly referred to as “synthesis gas” or “syngas”. Reformers of this type include some means for vaporizing, or evaporating, the liquid fuel prior to or as the fuel is mixed with the oxygen-containing gas, and if utilized the steam, components of the reformable reaction mixture.
In one known type of vaporizer for a liquid fuel reformer, liquid fuel at ambient temperature is directed as a spray against an electrically heated surface with vaporization of the fuel occurring upon contact with the hot surface. Liquid fuel vaporizers that operate on the principle of contact of the fuel with a hot surface, i.e., “contact vaporization”, are subject to the disadvantage that rapid introduction of ambient temperature fuel (so-called “cold fuel”) onto a hot surface can cause the fuel droplets to bounce off without vaporizing and fuel droplets that do adhere to the hot surface to decompose by pyrolysis. Either of these occurrences can result in the buildup of tars and/or coke that are inimical to the efficient operation of the reformer and, it may be added in the case of a reformer supplying hydrogen-rich reformate to a fuel cell system, the efficient operation of the fuel cell system as well.
It is known to vaporize liquid fuel in a liquid fuel reformer by heating the fuel to its vaporization temperature with hot gas resulting from the combustion of a portion of the liquid fuel with oxygen supplied as air. While a fuel vaporizer of this type avoids the drawbacks of contact vaporization noted above, it is subject to the disadvantage that the combustion reaction risks the formation of carbon black and/or other carbon-rich pyrolysis products such as tars and coke that over time will accumulate resulting in progressive degradation of the performance of the reformer of which the vaporizer is a part.
A need therefore exists for a fuel vaporizer for incorporation in a liquid fuel reformer that avoids the foregoing drawbacks of known vaporizer devices while providing effective and thermally efficient vaporization of all types of reformable liquid fuels.